The present invention relates to a fly by wire flight control system for a rotary-wing aircraft, and more particularly to a full authority fly by wire flight control system which accommodates an emergency landing scenario.
Fly By Wire [FBW] flight control systems are increasingly state of the art in the control of rotary-wing aircraft. The highly specialized control laws in a FBW flight control system provide functionality for all states of aircraft operation including ground state operation. Rotary-wing aircraft with a partial authority flight control augmentation system do not require mode changes when the aircraft is on the ground, because there is little potential for unwanted feedback into the control system. A full authority FBW flight control system, however, requires a specific surface contact mode to prevent undesired feedback into the control system. The surface contact mode transitions between a fully augmented normal flight control state and a ground state once the majority of the aircraft weight is supported on the ground.
The surface contact mode is initiated through weight-on-wheels switches on the landing gear. As the aircraft touches the ground, landing gear struts compress, and switches activate the ground contact state. There are, however, landing scenarios where the weight-on-wheels switches will not function such as when the landing gear cannot be extended due to a malfunction, or when the aircraft must be landed in water, e.g., ditched.
Accordingly, it is desirable to provide a fly-by-wire flight control system which can transition into a ground contact state during an emergency landing scenario when weight-on-wheel switches may not be usable. This state would be referred to as a surface contact override transition mode.